1. Field
The present invention relates to power generation systems, and specifically to a system and method for reducing crosstalk while signaling between the components in direct current distributed power generation systems.
2. Related Art
A photovoltaic power generation system may incorporate one or more photovoltaic panels with optional electronic modules attached thereto. An inverter connects to the photovoltaic panels or electronic modules. Power output from the photovoltaic panels or electronic modules is direct current (DC) power. The electronic modules may perform direct current DC-to-DC conversion. The inverter inverts the DC power output to alternating current (AC) power.
As previously disclosed by the present inventors in US patent application publication 2008/0147335, the DC power cables connecting inverters to photovoltaic panels and/or electronic modules may provide a communication channel between the inverters and the photovoltaic panels or modules. The communication channel between inverters and modules, allows monitoring of the performance of the modules for monitoring temperature, current, voltage and power output of a the photovoltaic modules and potential allows for control of the modules.
Typically, lengths of cables connecting the inverter to the panels or modules may be long and may contain one or several wire cores. Within a photovoltaic installation, a wire at positive potential and a wire at negative potential electrically associated therewith may be physically proximate thereto only at a point of connection to a piece of equipment. However, elsewhere in the photovoltaic field, the wires may be separated and not be within the same cable run. The topography of the distributed power generation system to a large extent dictates the installation and placement of cable runs. Physical proximity of wires not having an electrical association may increase the chances of the wires in the cables being subject to the effects of noise if those wires are to be considered for signaling by DC power line communications. Crosstalk is a type of noise which refers to any phenomenon by which a signal transmitted on a cable, circuit or channel of a transmission system creates an undesired effect in another cable, circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one cable, circuit or channel, to another. Crosstalk may also corrupt the data being transmitted. Typical known methods of preventing the undesirable effects of crosstalk may be to utilize the shielding of cables, modules, panels, inverters or using twisted pair cables. Additionally, filtering techniques such as matched filters, de-coupling capacitors or chokes may be used to prevent the undesirable effects of crosstalk. However, these typical ways of preventing the undesirable effects of crosstalk are typically unavailable or impractical for power line communications over DC lines in a power generation system and/or may be prohibitively expensive in terms of additional materials and/or components required.
In a photovoltaic power generation system, with power line communication over DC cables, it may be desirable to send a control signal between and an inverter and a particular photovoltaic module but no other modules. Crosstalk may cause the other photovoltaic modules in the power generation system to inadvertently receive the control signal which is of course undesirable.
Thus there is a need for and it would be advantageous to have a system and method of reducing cross-talk in DC power line communications in a distributed DC power generation system, e.g photovoltaic DC power generation system.
The term “memory” as used herein refers to one or more of read only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), FLASH memory, optical memory, e.g. compact disk, switches, random access memory (RAM), magnetic memory such as a hard disk or other memory types known in the art.
The term “direct current (DC) power source” as used herein refers to (DC) power source such as batteries, DC motor generator; switch mode power supply (SMPS), photovoltaic panels and/or photovoltaic panels operatively attached to a converter module such as a DC to DC converter.
The term “photovoltaic source” as used herein refers to a photovoltaic panel and/or a photovoltaic panel operatively attached to a electronic module which includes for instance a DC-to-DC converter. The term “electronic module” and “photovoltaic module” are used herein interchangeably and refer to a functional electronic circuit attached to a photovoltaic panel.
The term “noise” as used herein in a communication channel, includes any unwanted signal finding itself in the communication channel. Sources of noise may include radio frequency interference (RFI), mains electricity hum, unsuppressed switching voltages and crosstalk.
The term “crosstalk” as used herein refers to any phenomenon by which a signal transmitted on a cable, circuit or channel of a transmission system creates an undesired effect in another cable, circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one cable, a circuit, part of a circuit, or channel, to another.
The term “telemetry” as used herein refers to measurement, transmission and reception of data by wire, radio, or other means from remote sources. In the context of the present invention, telemetries are from the photovoltaic panels.
The term “transducer” as used herein refers to a device used for the conversion of one type of energy to another, for example, the device changes electrical energy in to electromagnetic energy and vice versa. The term “transducer” herein may also have functions of a sensor or detector. The terms “sensor” and “transducer” as used herein are used interchangeably.
The terms “signal”, “signaling” or “signaling mechanism” as used herein refers to a signal modulated on a carrier signal. The carrier signal may be an electrical or an electromagnetic signal. The signal may be a simple on/off signal or a complex signal which imparts information as data. For a modulated signal, the modulation method may be by any such method known in the art, by way of example, frequency modulation (FM) transmission, amplitude modulation (AM), FSK (frequency shift keying) modulation, PSK (phase shift keying) modulation, various QAM (quadrature amplitude modulation) constellations, or any other method of modulation. Although strictly, the terms “modulation” and “coding” are not equivalent, the term modulation and demodulation are typically used herein to include coding and decoding respectively.
The term “signal strength” as used herein refers to the magnitude of the electric field/current or voltage at a reference point that is a significant distance from a transmitting source. Typically, “signal strength” is expressed in voltage per length or signal power received by a reference point expressed in decibel (dB) per length (meter), dB-millivolts per meter (dBmV/m), and dB-microvolts per meter (dBμV/m) or in decibels above a reference level of one milliwatt (dBm).
The term “positive comparison” in reference to the comparison of two codes or two signals means equal within tolerances or thresholds or derivable one from the other in a known way.